Android Shape Drawable改变属性

Question

我有几个形状可绘制资源，我想用作按钮的背景，除了渐变开始和结束颜色以及描边颜色外，它们是相似的。问题是我不想为此可绘制对象创建多个类似的 XML 文件。

我想我可以像使用标签的样式一样继承可绘制的形状，但这是不可能的。

我找到了这个 Defining XML Parent Style of Gradient / Shape / Corners但我不明白它是如何工作的。他如何改变属性值？

有Using parents for drawable resources我发现我可以通过图层列表更改背景的外观，图层列表将一层一层地绘制可绘制对象。但是如何使用图层列表来处理渐变和笔触颜色？

我发现我可以在运行时更改按钮背景的外观，但可能有更简单的方法来做到这一点？

Answer 1

我最初的建议是不可行的。我以为 <shape>将返回 ShapeDrawable但我错了，这里是我将如何修改渐变。

点击按钮之前

点击按钮后，其背景发生变化。

这是主要 Activity

public class MainActivity extends Activity {

    Button button;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        button = (Button)findViewById(R.id.button);

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v)
            {
                try
                {
                    // you can use the GradientDrawable directly, check the docs for details,
                    // I extended GradientDrawable just to make myself look like a badass :)

                    MyReflection.invokeMethod(button, new Gradient(), "setBackground");
                } 

                catch (NoSuchMethodException e)
                {
                    e.printStackTrace();
                } 

                catch (InvocationTargetException e)
                {
                    e.printStackTrace();
                } 

                catch (IllegalAccessException e)
                {
                    e.printStackTrace();
                }
            }
        });

     }
}

使用对象获取新方法的实用方法来调用该方法，Drawable用作新背景，方法名称不带 ()例如 setBackground在旧版本上运行。反射很慢。谨慎使用。

/*
* We want to use reflection because the View.setBackground() method
* is only available on API level 16 and up.
* If you don't understand this, you can follow the tutorial provided by
* Oracle, just search for it on Google with the keyword "reflection tutorial"
*/

public class MyReflection {

    public static void invokeMethod(Object receiverObject, Drawable background, String methodName)
            throws NoSuchMethodException, InvocationTargetException, IllegalAccessException
    {
        Class<?> clazz = View.class;

        Method method = clazz.getMethod(methodName, Drawable.class);

        // Allowing non-public access call to this method.
        method.setAccessible(true);
        method.invoke(receiverObject, background);
    }
}

我的自定义渐变

/**
* I am extending the GradientDrawable just for fun, and also
* because I want to set the shader property for this drawable,
* you could, however, use the GradientDrawable directly.
*/
public class Gradient extends GradientDrawable {

    private Paint paint;
    private LinearGradient gradient;

    public Gradient()
    {
        super();
        // check the docs for LinearGradient for these parameters
        gradient = new LinearGradient(0,0, 100, 100, Color.BLUE, Color.GREEN,   Shader.TileMode.REPEAT);
        paint = new Paint();
        paint.setShader(gradient);
    }

    public Gradient(GradientDrawable.Orientation orientation, int[] colors)
    {
        super(orientation, colors);
        gradient = new LinearGradient(0,0, 100, 100, Color.BLUE, Color.GREEN, Shader.TileMode.REPEAT);
        paint = new Paint();
        paint.setShader(gradient);
    }

    @Override
    public void draw(Canvas canvas)
    {
        canvas.drawPaint(paint);
    }
} 

按钮的初始背景

<?xml version="1.0" encoding="utf-8"?>
<!-- The initial shape with just a solid yellow color -->
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">

    <solid
        android:color="#ff0"/>

</shape>